1. Field of the Invention
The present invention relates to a diaphragm forming at least one electrode of a condenser functioning as a differential pressure-detecting sensor in a condenser-type microphone detector mounted in, for example, a non-dispersive infrared analyzer for analyzing a gas and the like. The diaphragm is used as a pressure-receiving and dislocating member, which receives a pressure which causes it to be transformed and dislocated.
2. Description of the Prior Art
FIG. 12 is a schematic drawing showing one example of a general infrared gas analyzer. Referring now to this drawing, it has a measuring cell a into which a sample gas is continuously introduced, a reference cell b in which an inert gas (for example a N.sub.2 -gas or the like) is enclosed, a light source d for directing infrared rays onto said measuring cell a, and said reference cell b, respectively, a chopper e for periodically interrupting light from said light sources c and d, and a light-receiving chamber g upon which light which has passed through said measuring cell a and said reference cell b, respectively, is incident. A gas, which absorbs the energy of an incident infrared ray and is thus caused to be expanded, is enclosed in said light-receiving chambers f and g. A condenser-type microphone detector x for detecting a differential pressure between the two light-receiving chambers f and g is mounted between the two chambers. The pressure P.sub.f of the light-receiving chamber f and the pressure P.sub.g of the light-receiving chamber g is applied to said condenser-type microphone detector x through ducts h and i, respectively. The resulting differntial pressure signal is taken out and supplied to an outside circuit consisting of an amplifier j, a recorder k, an indicator l and the like.
Condenser-type microphone detectors having the following construction have been used for said condenser-type microphone detector x, functioning as said differential pressure-detecting means.
FIGS. 13(A) and 13(B) show such a detector having the most basic construction. As shown in FIG. 13(A), a fixed electrode 1 is provided which serves as a standard electrode, has a fixed electrode plate 1B provided with at least one air hole or slit m therein and electrode plate 1B is mounted on a first electrode-supporting base 1A. Base 1A is connected to the duct h carrying the pressure P.sub.f from said one light-receiving chamber f. A movable electrode 2 is provided in which a diaphragm 2B formed of a simple thin metallic film, for example a titanium film, as shown also in FIG. 13(B), is mounted on a second electrode-supporting base 2A. Base 2A is connected to the duct i carrying the pressure P.sub.g from said other light-receiving chamber g. The diaphragm 2B acts as a pressure-receiving and dislocating member which is transformed and dislocated by the differential pressure P.sub.g -P.sub.f between said light-receiving chambers f and g. An insulating spacer 3 is mounted between the diaphragms 2A and 2B to keep them in spaced opposed relationship.
However, with a condenser-type microphone detector x having such a conventional construction, since the diaphragm 2B which acts as the pressure-receiving and dislocated member of the movable electrode 2 has been formed of the simple metallic thin film, as above described, the tensile stress on the film can not help but be increased during deformation. Accordingly, there is a limit to the dislocation due to the differential pressure P.sub.g -P.sub.f which can not be increased, so that a compact and highly sensitive diaphragm 2B can not be obtained. In addition, since in order to give a uniform tensile force to the film during the deformation of the diaphragm 2B formed of the metallic thin film on said second electrode-mounting base 2A, a manual operation requiring great skill is necessary, and problems have also occurred in that a mass production is difficult and the manufacturing cost is very high.
A condenser-type microphone detector x' having a different construction has been recently proposed in, for example, Japanese Patent Application Laid-Open No. 133323/1985, and thus is shown in FIGS. l4(A) and l4(B). As shown in FIGS. l4(A) and l4(B), a fixed electrode 1' is provided which serves as a standard electrode. It has an insulating plate-like member 1B' provided with a large number of air holes or slits n formed in one half thereof, the upper half in this drawing, and an electrode plate p attached to an interior side thereof. A movable electrode 2' is provided which is formed of a diaphragm 2B' which serves as a pressure-receiving and dislocatable member, and which has an insulating plate-like member 2B' having a central movable portion 2b internally connected through two supporting portions 2c to an outside circumferential fixing portion 2a so as to be rotatable relative thereto. The plate-like member 2B' has a large number of air holes or slits o in one half thereof (the lower half in this drawing) and an electrode plate q is formed on the interior side of the upper half by plating, vapor coating or the like. The interior sides of plates 1B' and 2B' face each other, and the plates are fixedly held between a first electrode-supporting base 1A' connected to a duct h for receiving a pressure P.sub.f from said one light-receiving chamber f, and a second electrode-supporting base 2A' connected to a duct i for receiving a pressure P.sub.g from the other light-receiving chamber g, and are spaced by a spacer 3' so as to have a desired distance therebetween.
In a condenser-type microphone detector x' having such a construction, since the diaphragm 2B' acting as the pressure-receiving and dislocatable member of the movable electrode 2' has the central movable portion 2b rotatable around the two supporting portions 2c, it can be very highly sensitive and relatively compact in comparison with a detector having the above described basic construction as shown in FIGS. l3A and l3B, and does not have the deficiency due to the tensile force on the thin metallic film.
However, since a very large twisting resistance is required at said two rotary supporting portions 2c it is quite useless to form the diaphragm 2B' of a thin metallic film. In practice, it is formed of a quartz crystal which is an insulating material. Accordingly, its manufacture requires a very difficult and time-consuming micro forming technique, such as anisotropic etching, and it requires an additional installation step for the separate electrode plate q, so that it is unsuitable for mass production. In addition, since a quartz crystal having a high brittleness must be used, there is a problem particularly with respect to the endurance of the two rotary supporting portions 2C.